Tunable pulsed lasers using dye cells as the gain medium and diffraction gratings as the wavelength-selective element have been available since the early 1970s. These early lasers, however, had relatively broad linewidths, poor temporal and spatial beam properties and produced relatively low powers and/or energies In addition, these early lasers had relatively many parts and were difficult to align.
It was also discovered that mode-hopping and mode-beating of these tunable pulsed lasers occurred as the laser was tuned over its entire tuning range. Since output beams that exhibit mode-beating can cause undesirable responses in the materials into which they are introduced, a single longitudinal mode is to be preferred.
It is known that continuous-wave (CW) lasers can operate with very narrow bandwidths. However, to produce pulsed outputs from such lasers, it is necessary to pulse amplify the CW output into the desired pulses. The process of amplifying the output is inefficient and requires complicated circuitry.
Further, it has long been known that gain mediums based on dye cells are relatively short lived.
It is therefore desirable to have a simple pulsed laser that can produce tunable single-mode outputs over a very broad range of wavelengths at moderate powers for long periods of time.